The Texan only celebrated his 24th birthday in July, but he already has the Masters, US Open and British Open to his name.
Of every golfer to ever play the game, only Jack Nicklaus has won three different majors at such an early stage in his career. Only Tiger Woods has completed the set before his 25th birthday.
CNN Sport takes a look at the other greats that have completed a career grand slam in golf.
Bobby Jones (1930)
When Bobby Jones won every major golf championship in the same year back in 1930, the watching world struggled for words to describe the magnitude of his achievement.
It was at this moment that Oscar B Keeler -- an Atlanta Journal reporter who traveled over 120,000 miles covering every tournament stroke of Jones's career -- settled on a term previously used most often in the card game, Bridge.
Jones, just 28, had captured the British Open, the British Amateur, the US Open and the US Amateur -- every major "trick" available at the time. The notion of the golf "grand slam" was born.
It's said Jones, a Harvard graduate and lawyer by trade, placed a bet on himself achieving the unprecedented feat with a British bookmaker at odds of 50/1 at the start of the year.
And with the grand slam sealed -- at Merion Country Club, where he initially arrived onto the scene of at the age of 14 -- he retired from tournament golf.
It was some way to go out; nobody has ever won all four majors in the same year since.
Gene Sarazen (1935)
But that hasn't stopped others winning a career grand slam.
Since the inception of the Masters in 1934 -- overseen by Jones himself -- five men have achieved the feat in the modern era.
First came Gene "The Squire" Sarazen, an American credited with inventing the modern sand wedge.
Sarazen dominated the 1922 season, winning the US Open and PGA Championship in quick succession aged just 20.
It would, however, take a full decade for him to clinch the British Open. Sarazen took home the winner's share of £100 at the 67th Open Championship in 1932 -- the only time it was ever held at Prince's Golf Club in South East England.
He completed the set at Augusta National in 1935 aged 33, emerging victorious in just the second ever Masters tournament thanks to a final round double eagle at the par-5 15th now known as "the shot heard around the world."
Sarazen had been three shots off the lead until his albatross -- one of just four ever made at the Masters to this day -- and went on to win the resultant playoff with Craig Wood.
Ben Hogan (1953)
Already 34 years old when he won his first major, Ben Hogan had hit 40 when he conquered the career grand slam in 1953, winning the British Open at Carnoustie on the first and only occasion he entered.
That win was just part of a golden season for the Texan.
Renowned for his swing, Hogan might have joined Jones in the history books as a winner of all four majors in a single year, had the 1953 PGA Championship not clashed with the British Open.
Still, his "Triple Crown" season -- also encompassing victories at the Masters and US Open -- has only been emulated once since, by Tiger Woods a full 47 years later.
Gary Player (1965)
As the amateur championships faded from significance, the modern notion of the "grand slam" was popularized in 1960 by none other than Arnold Palmer.
It was thirty years on from the unparalleled achievements of Jones, and "The King" was midway through an extended cocktail hour with golf writer Bob Drum on board a flight to the UK.
As Palmer writes in his autobiography A Golfer's Life: "Bob Drum and I got to talking about Jones' great grand slam. Drum remarked to me that it was a shame that the growth of the professional game, among other things, effectively ended the grand slam concept as it had been known in Jones' day.
"'Well,' I said casually over my drink, 'why don't we create a new grand slam?'"
"What would be wrong with a professional grand slam involving the Masters, both Open championships, and the PGA Championship?'"
The idea spread like wildfire, but Palmer -- a seven-time major winner -- was never able to secure the PGA Championship to complete the set, placing second on three occasions.
Instead South Africa's Gary Player sealed the deal when he won the US Open in 1965 at the age of 29, six years on from his first major.
Victory at Bellerive Country Club that season saw Player become the first foreign-born winner of the US Open for 38 years.
It was the first and only time "the Black Knight" won the tournament but he certainly made it count. To this day, he remains the only non-American to boast a career grand slam in golf.
Jack Nicklaus (1966)
Jack Nicklaus joined the grand slam club aged 26 -- two years older than Woods -- when he won the 1966 British Open at Muirfield.
He might have done so even earlier.
The Golden Bear was midway through his 24th year when he won his third major at the 1963 PGA Championship. It took him another three years to add the final piece of the puzzle.
Not that he let up. Nicklaus, a record 18-time major winner, accomplished the "double" career grand slam in 1971 and the "triple" just seven years later.
The last of his three majors were secured over the age of 40, and his final title -- the 1986 Masters -- at 46.
Tiger Woods is the only other player to win all four majors at least three times over the course of his career.
Tiger Woods (2000)
As it stands, Woods is the youngest player in history to have achieved the career grand slam.
The Floridian was just 24 when he won the British Open at St Andrews in 2000 -- six months and seven days older than Spieth, should he emerge victorious at Quail Hollow Club come Sunday.
Woods held the world No. 1 spot from August 1999 to September 2004, and once again from June 2005 to October 2010 — longer than any other golfer in history.
He is the only player in the modern era to have held all four majors at the same time -- having won the 2000 US Open, British Open, PGA Championship and 2001 Masters in succession.
That period of dominance has since been nicknamed the "Tiger Slam," but even Woods didn't manage to emulate Jones by doing it in a single season.
Should Spieth win Sunday, he'll at least have one record under his belt.